Hypodermic injector



Dec. 17, 1957 R. P. scHERER ErA 1 2,816,544

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Dec.. 17, 1957 R. P. scHERER l-:TAL 2,816,544

HYPODERMIC mJL-:GTOPK` 2 Sheets-Sheet 2 Filed July 12. 1954 l" 4 Ill HYPODERMIC INJECTOR Robert Pauli Scherer, Grosse Pointe, and Anthony Venditty, Detroit, Mich., assignors to R. P. Scherer Corporation, Detroit, Mich., a corporation of Michigan Application July 12, 1954, Serial No. 442,614

Claims. (Cl. 12S-173) This invention relates to a needleless hypodermic injector capable of injecting a fine stream or jet of liquid medicament at high velocity through the epidermls. More particularly, the invention constitutes an improvement over the injector described in the copending application of Robert P. Scherer, Serial No. 94,579, led September 28, 1953, and now Patent No. 2,704,543. rlhe instrument described in that application is adapted to discharge liquid medicament from an ampule at two different pressure stages, an initial high pressure stage for causing the jet stream to distend the skin and penetrate to a predetermined depth, followed by a reduced pressure stage for completing transfer of the liquid from the ampule through the opening produced during the high pressure stage. The two pressure stages are produced by a spring-actuated dual plunger assembly comprising a primary plunger of small diameter slidably mounted within a secondary plunger having a diameter equal to that of the liexible rubber-like follower or stopper Within the bore of the ampule. The follower is cup-shaped and is adapted to expel liquid through a minute orifice in the end of the ampule as it advances down the bore. As the power Spring expands, the primary plunger exerts a force against the central portion of the bottom of the follower to distend that portion a short distance and simultaneously eject a small amount of liquid from the orifice in the ampule under high pressure. The magnitude of the pressure during the first stage determines the depth of penetration of the stream below the surface. After the primary plunger has traveled to the end of its stroke, which is relatively short, the secondary plunger engages the entire area of the bottom of the follower and moves the follower down the bore of the ampule to complete the injection at reduced pressure. The reduction in pressure, of course, is due to an increase in the area engaged by the plunger. The pressure during the second stage is just enough to feed the liquid through the channel made during the rst pressure stage.

Since the primary plunger only distends and does not move the follower, the follower does not travel down the bore of the ampule until engaged by the secondary plunger. Therefore, part of the energy supplied to the plunger to generate pressure is momentarily diverted in overcoming starting friction in advancing the follower. The result is that the pressure of the liquid jet does not drop directly from rst stage to second stage and then level olf, but dips below the normal second stage pressure at the point where the starting friction must be overcome, and thereafter increases to the normal second stage pressure. This reduction in pressure and subsequent sudden increase in pressure due to overcoming the friction of the follower in the ampule is highly undesirable because in some patients the resulting surge causes pain.

It is one of the objects of the present invention to provide an instrument for two-stage pressure injection in which the pressure is reduced to the second stage without the undesirable momentary drop just described.

1 r 2,816,544 EC Patented Dec. 17, 1957 Another object is to provide two pressure stages through a single plunger. These and other objects will become apparent from the following description and the accompanying drawing, in which:

Figure 1 is a longitudinal sectional view through an instrument illustrating the invention;

Figure 2 is a longitudinal sectional view through the instrument of Figure 1 showing the position of the parts of the plunger assembly at the end of the high pressure portion of the plunger stroke;

Figure 3 is a transverse section along the line 3 3 of Figure l; and

Figure 4 is a similar view of the lower portion of the instrument shown in Figure 1 illustrating a modification of the plunger assembly.

Broadly, this invention consists in the provision of a single plunger advanced by forces of two different magnitudes to produce the two pressure stages desired. Since pressure equals force divided by area, it is apparent that pressure may be increased either by increasing the force or decreasing the area. In the construction of the present invention the force on the ampule follower may be varied to produce the change in pressure. The change in force is accomplished by mechanically multiplying the force applied to the plunger during the iirst part of the stroke and then transmitting the force of the same magnitude directly to the plunger, without the aid of the multiplier, for the remainder of the stroke. By this means the pressure resulting from the multiplied force is high, whereas that resulting from direct transmission is relatively low. The ratio of the pressures may be controlled by changing the construction of the force-multiplying device.

For a detailed description of the invention, reference is now made to the drawing in which the numeral 10 designates a body housing most of the mechanism of the injector. A dosage sleeve 12 is screwed onto the threaded lower or ampule-containing end of the injector, and a winding sleeve 14 is rotatable on the upper end thereof. The sleeve 14 has an inturned flange 16 coacting with an annular ridge or ring 1S on the body 10 to prevent longitudinal movement in one direction relative to the body. A latch housing 20 is screwed into the rear or upper end of the winding sleeve 14 with a thrust bearing assembly 22 interposed between the body and the latch housing.

A release button cap 24 is threaded on the latch housing 20 and the entire assembly of the winding sleeve 14, latch housing 20 and cap 24 is held in assembled relation by a set screw 26 engaging all three parts and sealed in place, as best shown in Figure 3.

The dosage sleeve 12 has threaded on its lower end an ampule holder 30 adapted to receive an ampule having medicament 32 therein and a flexible cup-like follower 33, preferably made from an oil-resistant rubber, such as polychloroprene or the like. The ampule is provided with a reduced discharge nozzle 34 perforated by a minute discharge orifice 35. The ampule holder is covered by a resilient nose 36 which may also be made from polychloroprene rubber, Buna N or the like.

The internal mechanism of the injector includes the novel plunger construction of the invention which consists of a plunger ill having an integral head 42 slidably mounted within the bore of the dosage sleeve 12 and a complementary disc 50, also slidably mounted within the sleeve 12, adapted to nest with the recessed portion of the head 42. Force-producing means in the body, described hereinbelow, is transmitted to the plunger 4l) by means of a piston 67 rotatably secured to the head 65 of the screw 62. The head 65 is adapted to rotate within the opening in the top of the piston 67 against the heattreated disc or bearing 69. The upper edge 59 of the piston may be peened over, or otherwise suitably secured,

to prevent the piston from sliding off the head of the screw 62. The end of the piston 67 is adapted to fit accurately into flange-like restriction 51 of the central opening 54 through the disc 50. The disc 50 comprises the upper portion of a separable head for the plunger 40, and is tapered in steps which nest with a complementary stepped depression in the integral head 42, which terminates in a well 43 in the bottom thereof. The opening 54 inthe disc 50 cooperates with the well 43 in the head 42 to define a generally cylindrical cavity which is filled with a slug 55 of plastic material, such as rubber. rl`he plastic slug 55 is shaped to fit precisely in the cavity. The top central area 52 of slug 55 is engaged by the bottom surface of piston 67 through restriction 51. Area 52 is equal to the area of the bottom of piston 67. The bottom surface of slug 55 bears against the bottom of well 43 in the head 42. Force applied to the piston 67 is transmitted through'the closely confined slug to the plunger 40, the multiplication of the force being determined by the ratio of area of opening 51 (which equals area 52) to the area 43. This ratio may be modified as necessary for the pressure desired. The top surface 56 of the disc 50 bears against the bottom surface 91 of each of a plurality of posts 9b comprising part of the body 16, thus preventing the disc 50 from moving upwardly in the body when pressure is applied to the plastic material 55 by means of the piston 67. Instead the plunger head 42 is forced downwardly.

The flanged end 46 of the plunger 40 is adapted to slide within the bore of the ampule 34- to engage the follower 33 for ejecting liquid from the ampule. A rubber washer 44 is provided in the bottom of the cavity of the sleeve 12 to provide a resilient cushion for the plunger head 42 when it reaches the end of its stroke.

The mechanism for propelling the plunger 46 cornprises a nut 6), a screw 62 and a plurality of power springs 64 disposed around the screw 62 within the body 10. The nut 6i) is sleeve-like in character and has a cloverleaf shaped head 66 provided with spring seats for the springs 64, which springs at their opposite ends seat against a partition 63 of the body 10. The nut 60 has threads 61 at its upper end which cooperate with the threads of the screw 62. The nut 60 will not rotate with respect to the body 10, but is adapted to move longitudinally therein. The upper end of the screw as shown in Figure 1 is provided with a head 70 providing a latching shoulder 71. The screw head 70 terminates in a bifurcated portion which results in a pair of spaced blades 72, the head with its blades being slidable in a square opening 21 in the latch housing 29. As shown in Figure 3,

" the latch housing is provided with a cross slot 23 in which the latch 25 is pivotally mounted. For this purpose a pivot pin 27 is press-fitted in the latch and has its ends rotatable in the latch housing. The latch 25 substantially spans the width of the slot 23 and the space between the blades 72 of the screw and is of the shape shown in Figure l, having a latching shoulder 75 and a spring socket '76. A latching spring 77 has one end seated in the socket and its other end seated in an opposing socket 78 in the latch housing for tending to rotate the latch counterclockwise.

Slidably mounted in the release button cap 24 is a release button 80 having a cross bar 82 attached thereto and slidable in the slot 23 of the latch housing 20 and the space between the blades 72 of the screw 62 back of the latch 25. When the button 80 is depressed, the latch 25 is rocked against the bias of the spring 77. A latch roll 83, rotatably mounted in the latch housing, prevents the screw 62 which is biased upwardly from moving until the latch 25 is released, thus permitting the latch roll 83 to rotate out from under the shoulder 71.

VIn operation, the ampule 31 is placed within the holder 30 and screwed onto the` end of the injector. Winding sleeve 14 is rotated causing the screw 62 to turn and lift the nut `60 to compressthe springs 64 seated in the head 4 66. The dosage sleeve is then rotated to bring the ampule follower 33 into contact with the end 46 of the plunger 40. The parts are then in the position shown in Figure l. It will be noted that the piston 67 extends into the rcstricted opening 51 in the disc 50 just a shore distance below the face 56 of the disc, and is separated from the top surface 52 of the rubber slug 55. lt is preferable to provide a spacing of this kind between the piston and the slug to permit the piston to gain momentum before striking the slug so that the piston will strike with impact. Release accomplished by depressing the button which permits the latch roll 83 to rotate out from under the shoulder 71. The springs 64 immediately expand moving the nut 60 and the screw 62 carried thereby downwardly. The piston 67, fixed to the end of the screw 62, strikes the top 52 of the plastic slug 55 with great impact. Since the slug is substantially incompressible and closely confined, the action thereof becomes hydraulic in its effect. In fact, a liquid could be used in place of the plastic although the latter is preferred because it is easier to confine. The force applied to the surface 52 is multiplied at the surface 43 in proportion to the ratio of the areas 51 and 43. (Area of opening 51 equals area of surface 52.) Force from the piston 67, transmitted to the plunger 40 through the slug, moves the follower 33 downwardly in the ampule to expel liquid at high pressure. As the piston 67 descends, the integral head 42 of the plunger 40 is moved downwardly away from the disc 50 which cannot move upwardly because it is firmly supported by posts 96) of the body 10. The distance of separation between head 42 and disc 50 is to the distance the piston 67 descends, as the area 52 is to the area 43. For example, if the area 52 is one square unit and the area 43 is four square units, and the distance the piston 67 moves into -the slug is one unit, the distance of separation between the head 42 and disc 50 is one-quarter unit. This distance is designated by the numeral 76 in Figure 2.

As the springs expand the nut 61B travels downwardly carrying the screw 62 and the piston 67 with it. The piston 67 increases the pressure on the slug 55 causing itpto exert a multiplied force on the head 42. The head 42 moves the distance 76, at which point the nut 6o strikes the face 56 of the disc 50, and the whole assembly comprising the plunger 40, disc 50, slug 55, screw 62 and nut 66, continues to advance as a unit with the head 42 and disc 50 in separated relationship. As soon as the nut 66 in its descent picks up the disc 50', the force on plunger 40 is direct, i. e. not multiplied through the slug 55, and the liquid is expelled from orifice 35 at normal reduced pressure to complete the injection.

To unwind the screw 62 to bring it back to cocked position, the winding sleeve 14 is rotated. The screw 62 turns within the head of the piston 67 against bearing 69 so that the piston lifts from the top surface 52 of the slug. Even at the end of the stroke the springs impose a great force on the piston which would cause abrasion of the plastic if means were not provided for permitting the screw to move independently of the piston.

A modification of the plunger assembly of the instrument shown in Figure l is illustrated in Figure 4. The only change involves the size and the shape of the rubber slug through which the force is transmitted. rhe upper disc 95, which comprises the top portion of the separable head of the plunger, is similar to the disc 50 of Figure l. Likewise, the head 94 which is integral with the plunger 96 is similar to the plunger 40 of Figure l. The cavity defined by the openingthrough the disc ,and the recess in the head 94 is shaped like a cylinder having an outwardly flaring base, and is filled with accurately tting plastic slug 97. The area 98 of the top surface of the slug is to the area 99 of the bottom of thebase, as the forceapplied to the piston 67 is to the force exerted by the plunger 96'. The ratio of the areas in the particular form illustrated is one to three, thus producing in the plunger a three-fold increase in the force applied by the piston 67. The distance the head 94 separates from the disc 95 is one-third the distance the piston moves downwardly into the slug 97. The operation of this instrument is exactly the same as the operation of that shown in Figure 1.

From the foregoing description it becomes clear that the construction of the plunger assembly may be modified in various ways to change the ratio of the upper and lower areas of the confined plastic slug to produce any desired force multiplication. The invention is not intended to be limited to the specific forms illustrated other than as necessitated by the scope of the appended claims.

We claim:

1. In a hypodermic injector, an assembly comprising an elongated body, an ampule holder detachably connected to one end thereof and adapted to hold an orificed ampule, a plunger slidably mounted within said body and adapted for engaging and propelling a follower within the bore of said ampule to discharge liquid contents through the orifice, said plunger having a head integral therewith and containing a central recess, a disc slidably mounted within said body adjacent said plunger head and having a central opening therethrough which cooperates with said recess to define a cavity, the area of the bottom of said recess being greater than the area of the top of said opening, a plastic slug closely confined within said cavity and having the top surface thereof exposed through said opening, power means within said body including a nut and a central piston projecting above the face of said nut, said piston being adapted to slide within said opening to apply force to said top surface of the plastic slug for transmission therethrough to said plunger head, said nut being adapted to engage said disc to propel said disc and said plunger as a unit when said piston has descended into said opening, said power means also including means for storing driving energy therein, and means for suddenly releasing the energy thus stored to propel said plunger with a force of one magnitude when the piston is acting upon said slug and with a force of lesser magnitude when said nut is engaged with said disc.

2. The assembly of claim 1 in which said piston is rotatably mounted on a screw threadedly engaged with said nut.

3. In a hypodermic injector, an assembly comprising an elongated body, an ampule holder detachably connected to one end thereof and adapted to hold an orificed ampule, a plunger slidably mounted within said body and adapted for engaging and propelling a follower within the bore of said ampule to discharge liquid contents through the orifice, power means for propelling said plunger including means for storing the driving energy therein, means for suddenly releasing the energy thus stored to perform propulsion of the plunger and follower, force multiplying means including a confined plastic slug associated with said plunger and adapted to increase the force applied to the plunger during the first part of its stroke.

4. In a hypodermic injector, an assembly comprising an elongated body, an ampule holder detachably connected to one end thereof and adapted to hold an oriced ampule, a plunger slidably mounted within said body and adapted for engaging and propelling a follower within the bore of said ampule to discharge liquid contents through the orifice, said plunger having a head containing a central recess, a disc slidably mounted within said body adjacent said plunger head and having a central opening therethrough which cooperates with said recess to define a cavity, the area of the bottom of said recess being greater than the area of opening, a plastic slug closely confined within said cavity, power means for propelling said plunger including a piston adapted to engage said plastic slug through said opening, means for storing driving energy therein, and means for suddenly releasing the energy thus stored to propel said plunger with a multiplied force through said plug.

5. In a hypodermic injector, an assembly comprising an elongated body, a cylindrical chamber in one end thereof having a bore terminating in a minute orifice and adapted to hold liquid to be discharged from the ejector, a follower within the bore of said chamber, a plunger slidably mounted within said body and adapted for engaging and propelling said follower to discharge liquid contents through the orifice, power means for propelling said plunger including means for storing the driving energy therein, means for suddenly releasing the energy thus stored to perform propulsion of the plunger and follower, force multiplying means including a confined plastic slug associated with said plunger and adapted to increase the force applied to the plunger during the first part of its stroke.

No references cited. 

